Apoptosis is central to the pathogenesis of cancer, because mutations that suppress apoptosis promote tumor development and contribute to radiation and chemotherapy resistance. New treatments that restore apoptotic mechanisms are urgently needed for gliomas, which are largely incurable, and kill over 20,000 a year in the United States. This study focuses on a novel group of interacting proteins, centered on the multifunctional adapter protein SETA, which is restricted to malignant astrocytes and tumors in the adult brain. SETA binds AlP!, a regulator of apoptosis and binding partner of ALG-2, which is itself required for apoptosis. SETA also binds signaling proteins of the Cbl family and Grb2. Introduction of various SETA isoforms into normal astrocytes, in vitro transformed p53-/- astrocytes, and the glioma-derived cell line U87MG showed that SETA is itself a modulator of apoptosis. Full-length SETA protein protected astrocytes from UV-induced apoptosis, while shorter, putative dominant negative SETA proteins sensitized cells in these experiments. Together these data support the hypothesis that SETA expression in gliomas suppresses apoptosis and so contributes to the growth and treatment resistance of these fatal tumors. To investigate SETA further we propose to (1) characterize the molecular interactions between SETA and its binding partners by (i) in vitro binding studies, (ii) co-immunoprecipitation experiments, and (iii) studying sub-cellular localization. In addition we will (2) examine the mechanism by which SETA modulates apoptosis. In order to do this we will first determine (i) which molecular regulators of apoptosis are expressed by glia and glioma cells, and (ii) which apoptotic stimuli they are sensitive to. In the context of these findings we will (iv) test the hypothesis that SETA is an important modulator of apoptosis and (iv) identify which apoptotic signaling pathway SETA impacts. This study will contribute to the general understanding of how apoptosis is regulated at the molecular level, and through the novel protein SETA, reveal new points of intervention that can be exploited for therapeutic purposes to benefit brain tumor patients.